Calibrations and corrections of a modular cylindrical SPECT system (McSPECT-II)

The authors have developed a modular cylindrical SPECT system (McSPECT-II) for clinical brain imaging. This system features a stationary cylindrical detector and a rotating collimator. The cylindrical detector is comprised of 120 NaI(Tl) crystal bars coupled to a circular array of PMTs. The output signal from each PMT is digitized by an ADC. The position calculation and corrections are performed using software and precalculated lookup tables on a Pentium-based PC. The collimator has four quadrants, and each quadrant consists of a parallel array of 25 collimator units. The four corner wedges between adjacent quadrants are utilized to accommodate line sources for system calibrations. The authors report the calibration and correction procedures developed for the McSPECT-II system. These procedures include: (1) PMT gain normalization, (2) azimuth bar identification, (3) energy correction, (4) axial linearity correction, and (5) uniformity correction. Results of these calibrations and corrections on data acquired by imaging various phantoms are presented.